This invention relates to a mobile working apparatus for doing works such as inspections and machining operations on structures such as nuclear reactor structures and a working method of operating such an apparatus.
Intra-nuclear-reactor working apparatuses are generally used for intra-reactor operations such as inspections, examinations and preventive maintenances of the inner surface of nuclear reactor pressure vessels and intra-reactor structures. Particularly, when the weld line found on the bottom of an annular part sandwiched between the pressure vessel inner wall and the shroud of a boiling water nuclear reactor is the target of operation, the operation faces various problems such as a limited working space and a long working time because it is difficult to access the target that is located in a very narrow area. Various intra-nuclear-reactor working apparatuses have been proposed to carry out such an operation in a short period of time and secure a larger working space.
Firstly, an intra-nuclear-reactor working apparatus comprising a slim self-propelled apparatus main body that is adapted to move on a shroud support plate, adhering to the wall surface of a nuclear reactor pressure vessel, a shroud support cylinder or a jet pump by suction, in order to inspect the weld line found on the bottom of an annular part is known (See Japanese Patent Application Laid-Open Publication No. Hei 11-174192, the entire content of which being incorporated herein by reference).
The apparatus has an inspection mechanism section that includes an airtight chamber for maintaining the orientation by buoyancy, a wall surface pushing means using a thruster and flowing water, a traveling means such as a crawler and inspection means such as various sensors. Thus, the apparatus runs by means of the crawler arranged at the bottom of the apparatus as it adheres to the wall surface so as to be guided by and move along the wall surface. Additionally, the apparatus gauges the distance from the inspection apparatus to a lateral surface of a jet pump diffuser by means of a non-contact range finder and identifies its relative position. At the same time, it identifies its absolute position on the shroud support plate from the distance covered by the crawler.
Secondly, intra-nuclear-reactor working apparatuses adapted to move on a shroud support plate between a shroud support cylinder and a jet pump adaptor by means of a pair of crawlers in order to inspect a weld line and clean a target area are also known (See Japanese Patent Application Laid-Open Publication Nos. Hei 11-109082, Hei 10-221484 and Hei 9-15376, the entire contents of which being incorporated herein by reference).
The apparatus described in Japanese Patent Application Laid-Open Publication No. Hei 11-109082 comprises a traveling mechanism section that is dimensioned to allow the apparatus to move in a narrow area and an independent inspection unit including an inspection camera and an ultrasonic search device, in which the inspection unit is coupled to and pulled by the traveling mechanism section. The apparatus described in Japanese Patent Application Laid-Open Publication Nos. Hei 10-221484 and Hei 9-15376 comprises a similar traveling mechanism section that is dimensioned to allow the apparatus to move in a narrow area and adapted to move on a shroud support plate by means of the nozzle mounted thereon for sucking and cleaning operations. These apparatuses can clean a region right below the jet pump riser pipe pinched by a jet pump adaptor.
Thirdly, an intra-nuclear-reactor working apparatus comprising a guide section formed so as to match the radius of curvature of the outer surface of a jet pump diffuser and a positioning mechanism for rigidly securing the apparatus by extruding an extrusion member toward a nuclear reactor pressure vessel to apply reaction force to the guide section for the purpose of ultrasonic inspection of detecting flaws of the welded sections of the lower ends of a jet pump adaptor at the bottom of an annular part is also known (See Japanese Patent Application Laid-Open Publication No. Hei 11-326291, the entire contents of which being incorporated herein by reference).
Unlike the above-described mobile inspection apparatus, this inspection apparatus is rigidly secured to a jet pump diffuser and is adapted to drive the inspection head for the purpose of ultrasonic inspection of detecting flaws by means of the head drive mechanism mounted in it. This apparatus is adapted to be rigidly and reliably secured to improve the accuracy of the inspection head scanning operation and hence the accuracy of inspection.
When, for example, inspecting the weld line of an intra-reactor structure such as a shroud in the water in a nuclear reactor by means of any of the known intra-nuclear-reactor working apparatuses by ultrasonic means, a phased array ultrasonic probe or the like is mounted on a vehicle that is designed to move, adhering to the wall surface by sucking, for the purpose of conveying and positioning the probe and examining the target of inspection. Additionally, a scanning mechanism having a certain degree of freedom of adjustment is employed and mounted on the vehicle for the purpose of remotely adjusting the operating position and the attitude of the probe in the inspection.
With such a combination of a vehicle and a scanning mechanism, it is possible to examine weld lines having a large radius of curvature such as those of both the inside and the outside of a shroud without giving rise to any interference of the scanning mechanism with the intra-reactor structures including the shroud and the jet pump, because the inspection sensor requires adjustment only to a slight extent. Furthermore, the risk of interference with the intra-reactor structures is low, if the scanning mechanism is fitted to the bottom side or the top side of the adhering and moving vehicle to increase the overall dimensions. Additionally, the combination of the adhering and traveling vehicle and the scanning mechanism can also be used for operations other than inspections such as cleaning operations, grinding operations and polishing operations as well as operations for improving stresses by means of laser peening involving a small reaction force. Laser peening refers to a preventive security treatment of irradiating a laser beam to or near a weld line in water in order to transform the tensile residual stress of the surface of a structure into compressive residual stress.
However, the use of a combination of a vehicle and a scanning mechanism for operations including those of examining the weld lines of shroud support cylinders and shroud support plates and the weld lines of nuclear reactor pressure vessels and shroud support plates that are found in narrow areas such as the bottom of an annular part entails the following problems.
When examining such weld lines, for example, the inspection sensor has to be made to follow the fillet-welded section showing a radius of curvature of about 15 mm so that the probe is required to change its position and attitude to a large extent. However, the space where a scanning mechanism can operate is dimensionally limited, and hence it is necessary to check the configuration, the structure and the dimensions of the scanning mechanism so that the inspection sensor may not interfere with the jet pump adaptor, if the position and the attitude of the inspection sensor are changed to a large extent.
Additionally, a sensing line is arranged between the shroud and the jet pump at the side of the shroud of the bottom of the annular part. Therefore, the overall length of the adhering and moving vehicle and that of the scanning mechanism mounted on it have to be reduced so that they may not interfere with the jet pump sensing line and the bracket anchoring it when they are moved peripherally along the shroud.
With the method of identifying the absolute position on the shroud support as described in Japanese Patent Application Laid-Open Publication No. Hei 11-174192 that is referred to above as prior art, it is conceivable that a traveling error occurs when the crawler slips in a region that is not covered by the jet pump diffuser. Additionally, in the area where the gap between the jet pump diffuser and the shroud support cylinder and the wall of the nuclear reactor pressure vessel is smallest, the gauging distance of the non-contact range finder relative to the moving distance along the wall surface is small, and thus a gauging error can occur depending on the adhering condition of the inspection apparatus to the wall surface. Therefore, it is reasonable to have apprehension of a degraded accuracy of gauging the traveling distance.
While all the intra-nuclear-reactor working apparatuses described in Japanese Patent Application Laid-Open Publication Nos. Hei 11-109082, 10-221484 and 9-15376 can move in narrow areas, they require means for highly accurately identifying the absolute position of a spot on the shroud support plate. With the intra-nuclear-reactor working apparatus described in Japanese Patent Application Laid-Open Publication No. Hei 11-326291, it is necessary that the apparatus for conveying and positioning the working equipment needs to be self-propelled in order to cover a large working area in a short period of time for the intra-nuclear-reactor working apparatus.
In view of the above-identified problems of the prior art, it is therefore an object of the present invention to provide a working apparatus and a working method that are adapted to perform accurate positioning operations in a narrow environment, such as, in the water in the nuclear reactor and complex scanning operations for various pieces of working equipment such as inspection sensors and can secure a large working area within a short period of time and reduce the overall working hours.